Probing the surface of oxidized carbon nanotubes by selective interaction with target molecules

• Linear correlation of surface coverage by quinonyl groups and CNT oxidation degree
• Increase of anodic and cathodic current from dopamine with CNT oxidation degree
• Cathodic current from hydroquinone is not affected by CNT oxidation degree.
• Quinonyl groups at oxidized CNT improve interactions with amine or hydroxyl groups.
• Molecular modeling emphasizes the key role of hydrogen bonding.

Screen printed carbon electrodes (SPCE) were modified with pristine and oxidized carbon nanotubes (CNTprist and CNTox, respectively). The extent of CNT oxidation evaluated by TGA increased with the time of reflux in nitric acid. The CNTox surface coverage by quinoid/phenolic functional groups was quantified by their voltammetric response at low redox potentials. Cyclic voltammetry was performed with SPCE-CNTox on solutions of hydroquinone, dopamine and ferricyanide used as model compounds. The sensitivity of reduced/oxidized forms of these molecules to the oxygen-containing functional groups of the CNTox was evaluated by the current intensity. Compounds with phenol/amine groups show a large increase of the current intensity with increasing CNT oxidation, while for carbonyl containing compounds only a negligible effect was perceived. Molecules that can hydrogen bond to the CNT functional groups interact better with the electrode surface, and this is supported by theoretical calculations. This showcases the use of CNTox modified SPCE for selective sensing.

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